In the field of laser processing, more and more fiber lasers have been used according to a recent increase in their power.
Here, a decrease in power of excitation light, an increase in loss occurring in an optical fiber, or the like may cause a decrease in power of light outputted from a fiber laser. Furthermore, while an object is being processed (an object is being irradiated with laser light) with use of the fiber laser, light reflected by the object may return to the fiber laser. This may cause an oscillation state of outputted light to be unstable, and may accordingly cause a variation in power of the outputted light. That is, as illustrated in FIG. 9, power of light outputted from the fiber laser may vary due to an effect of light reflected by an irradiated object. Therefore, in any of the above cases, since power of outputted light varies from original power, a processing characteristic is deteriorated.
In view of the above, the fiber laser is necessary to be configured such that a light power monitoring device monitors power of outputted light. For example, in a case where power of outputted light varies, such a variation in power of the outputted light is dealt with by adjustment to intensity of light which is caused to enter the optical fiber, depending on the power of the outputted light monitored.
As the light power monitoring device, one that is disclosed in Patent Literature 1 is, for example, known. FIG. 10 is a view schematically illustrating a main part of a light power monitoring device disclosed in Patent Literature 1.
According to a conventional light power monitoring device 101, optical fibers F1 and F2 are connected to each other at a connection 113 (see FIG. 10). The optical fibers F1 and F2 are provided on a reinforced member 115 in a state where the optical fibers F1 and F2 are covered by a high-refractive-index resin layer 114.
A reflected light detecting device 116 and an outputted light detecting device 117 are provided in a vicinity of the high-refractive-index resin layer 114, which covers the optical fibers F1 and F2. The reflected light detecting device 116 detects power of light which is part of backward-propagating light that has propagated through the optical fiber F2 in an input direction (in a direction in which the backward-propagating light propagates so as to be away from an irradiated object) and which has leaked from the connection 113. The reflected light detecting device 116 is provided on a side of the connection 113 which side is located downstream in the direction in which the backward-propagating light propagates. Meanwhile, the outputted light detecting device 117 detects power of light which is part of forward-propagating light that has propagated through the optical fiber F1 in an output direction (in a direction in which the forward-propagating light propagates so as to be away from a light source) and which has leaked from the connection 113. The outputted light detecting device 117 is provided on a side of the connection 113 which side is located downstream in the direction in which the forward-propagating light propagates. Power of leaking light detected by the reflected light detecting device 116 is essentially proportional to power of light reflected by the irradiated object which light enters the fiber laser again, whereas power of leaking light detected by the outputted light detecting device 117 is essentially proportional to power of light outputted from the fiber laser.